The present invention relates to a gyrotron device for generating a beam of an electromagnetic wave and, more particularly, it relates to a gyrotron device applied to the electron cyclotron resonance heating, i.e., heating plasma in a nuclear fusion reactor with the electromagnetic wave.
FIG. 1 shows a gyrotron device of this type, whose construction will be briefly described below.
The gyrotron device comprises an electron gun 1 for emitting an electron beam in the direction of arrow Z, a magnetic coil 2 for giving a cyclotron movement to electrons in the electron beam emitted from the electron gun 1, a cavity resonator 3 for resonating the electromagnetic wave generated from the electron beam, and an output section 5 for transmitting the electromagnetic wave through an output window 4.
When the beam of an electromagnetic wave with a frequency higher than 100 GHz and of 10 MW is supplied from the output section 5, using the gyrotron device with the above-mentioned cavity resonator 3, the resonating frequency of the electrons in the cavity resonator 3 is so high that the resonator 3 cannot have an inner diameter large enough to withstand Joule heat to a tolerable level. The inner wall area of the cavity resonator 3 must be made small accordingly. As a result, the ohmically heated inner wall surface of the cavity resonator 3 inevitably receives an extremely high heat load (&gt;1 KW/cm.sup.2). Therefore, it is practically impossible for this gyrotron device to supply a beam of continuous or long pulse electromagnetic waves having a frequency higher than 100 GHz and of 10 MW. A complex system having a plurality gyrotron devices must be used to achieve the electron cyclotron resonance heating of fusion plasma.
In the above-mentioned gyrotron device, the beam of electromagnetic wave is emitted through the output window 4 in an optional direction. This requires the use of a waveguide for transmitting the beam to a desired place. When the beam of electromagnetic wave is transmitted in this manner through the waveguide, its energy gradually decreases. In other words, the transmission efficiency of the electromagnetic wave beam is reduced. In addition, if the beam of electromagnetic wave is transmitted through the waveguide, it is difficult to focus the beam onto a desired object. This is also the reason why the above-mentioned gyrotron device is unfavourable for heating the plasma in the nuclear fusion reactor.
Another type of a gyrotron device is known which uses a Fabry-Perot resonator. This device is called "quasi-optical gyrotron". The axis of its resonator is perpendicular to those of magnet coils which generates a magnetic field to guide an electron beam emitted by an electron gun. The device is thus non-axisymmetric, which requires a complicated positional adjustment of mirrors, the electron gun, magnet coils, and the like. The above-mentioned 10 MW-100 GHz gyrotron device also requires a large Fabry-Perot resonator to withstand a mirror heat load. Hence, large-sized magnet coils must be used in the high-power quasi-optical gyrotron, which inevitably raise the cost of manufacturing the quasi-optical gyrotron.